In U.S. Pat. No. 4,184,861 which is hereby incorporated by reference, a process is disclosed for manufacturing a B.sub.2 O.sub.3 and CaO containing glass. The process essentially comprises converting glass forming batch ingredients, including calcined colemanite, into agglomerates, heating a bed of such agglomerates in a chamber by direct contact with gaseous combustion products so as to produce heated non-aggregated agglomerates and then supplying such agglomerates to a glass melting furnace. That patent also recognizes that there may be excess sensible heat in the combustion products which are passed through the bed of agglomerates and in order to recover some of that sensible heat, a heat exchanger is provided in the chamber containing the bed of agglomerates. Such process has also been practiced in the past by diluting the combustion products with ambient air to decrease the temperature of the gases leaving the bed-containing chamber.
It is also known in the art that when manufacturing such B.sub.2 O.sub.3 and CaO containing glasses, it is necessary that calcined colemanite be employed. Otherwise should the raw colemanite be employed there is a severe danger that when the agglomerates are heated they will disintegrate because of the violent release of the chemically bound water in the raw colemanite. Such water release will generally occur when the colemanite is heated to a temperature in excess of its decrepitation temperature, which typically is somewhere in excess of about 390.degree. C. Since it is desirable to heat the agglomerates to as high a temperature as possible but yet without causing the agglomerates to aggregate into a mass as, for example, would ocur if they were heated in excess of their melting or softening point, it has been necessary in the past to either purchase such calcined colemanite or to separately treat such colemanite prior to use. Obviously such additional treatment serves to increase the raw material costs of the batch and consequently the entire glass manufacturing process.
The present invention recognizes this deficiency and has as its object to provide for a more economical glass manufacturing process.
More specifically, the present invention provides for a glass manufacturing process which includes an in-situ calcination of colemanite to thereby take advantage of the excess sensible heat in combustion products and minimize raw material costs. Even yet more specifically, the present invention provides for an improvement in the above type indicated process by passing raw colemanite through the chamber containing the bed of agglomerates with the raw colemanite being passed through the chamber in indirect heat exchange relation to the combustion products and the agglomerates of the bed so as to heat the raw colemanite to a temperature in excess of its decrepitation temperature and then withdrawing the decrepitated, or calcinated colemanite, from the chamber. Such withdrawn or calcined colemanite then may be employed to supply at least a portion of the calcined colemanite needed for the batch.